Friday, 30 March 2012

The atmosphere of WASP-24b.

WASP-24 is an F-type star in the constellation of Virgo, 1076 light years from Earth. It has an effective temperature of 6075 K, compared to 5778 K for our Sun, is 1.13 times as massive as the Sun and has 6.32 times the Sun's volume. In 2009 a Hot Jupiter type planet was discovered orbiting WASP-24 by the SuperWASP planetary survey. This planet, WASP-24b, orbits the star at a distance of 0.0359 AU (3.59% of the distance between the Earth and the Sun), completing one orbit every 56.2 hours and is 1.01 times as massive as Jupiter, with 11 times Jupiter's volume (it is much less dense than Jupiter because it is much hotter, due to the heat from the nearby star, and therefore occupies more volume).

WASP-24b, compared to the planets of our Solar System. The Visual Exoplanet Catalogue.

In a paper published in the online arXiv database at Cornell University Library on 27 March 2012, and accepted for publication in the journal Astronomy & Astrophysics, a team of scientists led by Alexis Smith of the Astrophysics Group at Keele University describe the results of a study of the atmosphere of WASP-24b, using the Spitzer Space Telescope and the CAHA 2.2-m telescope at Calar Alto, Spain, combined with data previously collected by the SuperWASP-N and WASPSouth telescopes, the Liverpool, Faulkes North and Faulkes South Telescopes, and the Nordic Optical Telescope.

Smith et al. analyzed data from occultations of WASP-24 by WASP-24b, that is to say times when the planet passed in front of the star, in order to determine how shining through the atmosphere of the planet altered light from the star. From this they were able to determine that the atmosphere of WASP is reasonably clear; whereas other Hot Jupiter type planets have been shown to have opaque clouds of titanium and vanadium oxides.

From this they deduct that WASP-24b lacks a thermal inversion, a cool layer above and bellow which the temperature rises. On planets such as Earth or Jupiter, where such inversions exist, gasses precipitate out as liquids (or sometimes solids) in this layer, forming clouds. On WASP-24b, however, this will never happen, liquids that evaporate here will never reach a cool layer in the atmosphere, and will not precipitate back out, either remaining as gasses in the atmosphere, or being lost into space.

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